Tdm fmcw radar apparatus and signal processing method of apparatus

ABSTRACT

Transmitting antennas and receiving antennas are arranged such that a plurality of virtual antennas have the same position in a time-division-multiplexed (TDM) frequency modulated continuous wave (FMCW) radar apparatus. At least three peculiar chirps, at least one of which is included in a chirp loop of each of waveform signals transmitted by the plurality of virtual antennas having the same position, are respectively positioned in consecutive time slots and have different periods. A Doppler frequency may be uniquely determined from phase difference values between the at least three peculiar chirps respectively positioned in consecutive time slots measured from FMCW radar signals received at the plurality of virtual antennas.

This application claims priority from Korean Patent Application No.10-2021-0171135, filed on Dec. 2, 2021, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND 1. Field

A signal processing technique for a time-division-multiplexed (TDM)frequency modulated continuous wave (FMCW) radar apparatus is disclosed.

2. Description of Related Art

A multiple-input-multiple-output (MIMO) frequency modulated continuouswave (FMCW) radar apparatus achieves improved angle resolution at lowcost using multiple transmitting antennas and multiple receivingantennas. A time-division-multiplexed (TDM) MIMO radar apparatusdistinguishes a transmission waveform signal at the receiving antennausing a time-division multiplexing (TDM) scheme.

Description of FIG. 1

FIG. 1 illustrates an antenna array, which is composed of TXtransmitting antennas and RX receiving antennas, in an exemplary FMCWradar apparatus. In the exemplary TDM FMCW radar apparatus, the TXtransmitting antennas sequentially transmit an FMCW radar waveformsignal, and each transmitted FMCW radar waveform signal is reflected bya target and simultaneously received by the RX receiving antennas. Thetransmitting antennas and the receiving antennas are generally linearlyarranged at equal intervals, but may also be non-linearly arranged atnon-uniform intervals. As illustrated in the drawing, when a jthreceiving antenna receives a signal transmitted by an ith transmittingantenna, substantially the same signal as a signal in a case in which avirtual transmitting/receiving antenna is positioned at a position of(i, j) may be acquired. The virtual transmitting/receiving antenna is acase in which a transmitting antenna and a receiving antenna arepositioned in substantially the same place, and is referred to herein asa “virtual antenna.”

Description of FIG. 2

FIG. 2 is a diagram illustrating an example of range-Doppler processingfor estimating a range and a velocity from a TDM FMCW radar signal. Inthe TDM FMCW radar apparatus, one frame is composed of Nc chirps whichare repeatedly transmitted N_(Loop) times in a time division scheme fromeach of the N_(TX) transmitting antennas. That is, N_(C)=N_(TX) xN_(Loop). As illustrated in the drawing, the range-Doppler processing isequally performed for all virtual antennas. For example, in the TDM FMCWradar apparatus having an array composed of N_(TX) transmitting antennasand N_(RX) receiving antennas, the range-Doppler processing asillustrated in FIG. 2 may be performed for each of N_(TX)×N_(RX) virtualantennas.

As illustrated in the drawing, when the transmitting antennassequentially transmit an FMCW radar waveform signal, a receiving antennaRX₁ receives all reflected waves reflected from one or more targets likeother receiving antennas. A phase difference between a signaltransmitted from the transmitting antenna and a signal received at thereceiving antenna depends on a range from the transmitting antenna tothe receiving antenna via the target. A frequency difference betweentransmitting and receiving signals is referred to as a beat frequency,and this beat frequency may be estimated from a position of a peak, thatis, an FFT index, of output coefficients of a range fast Fouriertransform (FFT). Since the beat frequency has a one-to-onecorrespondence with the range to the target, the range to the target maybe estimated by estimating the beat frequency.

In FIG. 2 , a signal of a virtual antenna at a position of (0, 1), thatis, a virtual antenna in a case in which a 1st receiving antennareceives a signal transmitted by a 0th transmitting antenna will bedescribed as an example. First, range FFT processors 210-1 to210-N_(Loop) perform intra-chirp processing.

A difference between a transmission signal transmitted in a first chirploop of a frame from a transmitting antenna TX₀ and a signal that isreflected by a target and received by a receiving antenna RX₁ issampled, transformed into a frequency domain by the range FFT processor210-1 in units of chirps, and stored for each coefficient in a buffer230-1. A difference between a transmission signal transmitted in asecond chirp loop of the frame from the transmitting antenna TX₀ and asignal that is reflected by the target and received by the receivingantenna RX₁ is sampled, transformed into a frequency domain by the rangeFFT processor 210-2 in units of chirps, and stored for each coefficientin a buffer 230-2. A difference between a transmission signaltransmitted in a last chirp loop of the frame from the transmittingantenna TX₀ and a signal that is reflected by the target and received bythe receiving antenna RX₁ is sampled, transformed into a frequencydomain by the range FFT processor 230-N_(Loop) in units of chirps, andstored for each coefficient in a buffer 230-N_(Loop). The beat frequencymay be estimated through a process of finding a position of a peak,which is a shaded portion in the drawing, among coefficients stored inthe buffer, and from this, a range to the target may be obtained.

Meanwhile, when the target moves, a range between the radar apparatusand the target varies with time, and which is referred to as rangemigration. The range migration results in a change in a phase of theFMCW radar signal, and the degree of phase change is determined by aradial speed of the target. Accordingly, the radial speed of the targetmay be estimated by observing the phase change over time. As the totaltime for observing the phase change increases, even a small phase changemay be detected, so that a radial speed resolution is improved. On theother hand, as an interval for observing the phase change is reduced, afaster change may be detected, so that a limit of a detectable radialspeed is increased.

In order to estimate the range and the radial speed of the target fromthe signal received from one virtual antenna, a 2-dimensional spectralestimation scheme such as a two-dimensional (2D)-FFT or 2D-multiplesignal classification (MUSIC) is applied to a range-Doppler matrix. Arange-angle matrix is obtained from the MIMO antenna array, and at thispoint, a dimension of an angle is increased as much as a size of avirtual array.

In the example of FIG. 2 , each of Doppler FFT processors 250-1 to 250-Mperforms inter-chirp processing. Each of the Doppler FFT processors250-1 to 250-M receives as many output coefficients as the number of therange FFT processors 210-N_(Loop), that is, N_(Loop) output coefficientscorresponding to the same frequency, performs FFT on the outputcoefficients, and stores the transformed coefficients in a 2D buffer270. As many as the number of the output coefficients of the range FFTprocessors 210-1 to 210-N_(Loop), that is, M Doppler FFT processors250-1 to 250-M are provided. The buffer 270 stores range-Dopplerspectrum values obtained through a range FFT and a Doppler FFT. ADoppler frequency may be determined by identifying a position of a peak,for example, a shaded portion in the drawing, from the Doppler FFToutput spectrum stored in the buffer 270, and the radial speed of thetarget may be obtained from the Doppler frequency.

The Doppler FFT is applied to signals captured from the same TX-RXchannel or virtual antenna. Signals received from different channelshave different initial phases due to physical positions of thetransmitting and receiving antennas respectively corresponding to thechannels and an angle at which the target is positioned. Thus, a TDMFMCW system should always use only a signal obtained from the samechannel as a Doppler FFT input thereof in order to purely observe only aphase change according to a time change.

In the TDM FMCW system, when a length of one chirp is expressed asT_(chirp), a time difference between input samples of the Doppler FFTbecomes T_(loop)=T_(chirp) × N_(TX), because radio waves are transmittedsequentially from the N_(TX) transmitting antennas. At this point, whena range change rate due to a movement of the target, that is, the radialspeed, is expressed as v_(r), the Doppler frequency is given asf_(d)=2v_(r)/λ. Here, λ refers to a length of one wavelength. At thispoint, when a phase difference between the input samples of the DopplerFFT is expressed as Δf, a relationship of Δf=2πf_(d)T_(loop) isestablished.

In order to estimate a spectrum without having an aliasing phenomenon,sampling should be performed at least twice during one period accordingto the Nyquist sampling theory. This means that the phase differencebetween the samples should be within ±π. That is, in order to normallyestimate the radial speed of the target, the following conditions shouldbe satisfied,

|2πf_(d)T_(loop)|< π .

Since T_(loop) is always a positive number, by using a relationship off_(d) = 2v_(r)/λ, Equation (1) may be expressed as follows,

$\left| v_{r} \right| < \frac{\lambda}{4T_{loop}}_{.}$

That is, in the TDM FMCW, as the number of the transmitting antennasincreases, T_(loop) increases, and thus a maximum value of a measurableradial speed in an aliasing-free condition decreases in proportion tothe number of the transmitting antennas. For example, in a case of a 77GHz radar system in which there are 12 transmitting antennas and alength of one chirp is 40 ms, the maximum measurable radial speed ismerely about +/-7.3 km/h.

FIG. 3 illustrates velocity spectra that may be estimated from a DopplerFFT output spectrum. As illustrated in the drawing, the velocity spectraestimated from the Doppler FFT output spectrum include an observablespectrum and an aliased spectrum, and the velocity obtained from thesemay include a true velocity and a measured velocity, and thus a Dopplerambiguity problem arises. Thus, as illustrated in FIG. 3 , it isdifficult to accurately estimate the radial speed of the target due tothe aliasing phenomenon when the target moves beyond a maximummeasurable radial speed limit as in the example of FIG. 3 . Sinceincorrectly estimating the radial speed of the target has a decisiveeffect on an error in estimating the angle of the target, such a Dopplerambiguity problem must be solved.

A method for solving such a problem has been disclosed in the relatedart (Roos, Fabian, et al. “Enhancement of Doppler unambiguity forchirp-sequence modulated TDM MIMO radars.” disclosed at the 2018 IEEEMTT-S International Conference on Microwaves for Intelligent Mobility(ICMIM). IEEE, 2018, or Schmid, Christian M., et al. “Motioncompensation and efficient array design for TDMA FMCW MIMO radarsystems.” disclosed at the 2012 6th European Conference on Antennas andPropagation (EUCAP). IEEE, 2012). These papers have proposed an antennaarrangement of a particular structure in order to separate phaserotation due to the Doppler effect, and phase rotation components thatare determined by a position of a target and a position of a virtualantenna. These methods primarily estimate a radial speed of the targeton a range-Doppler spectrum, and estimate the radial speed of the targetagain using information about a phase change between the virtualantennas. However, such a method must design antennas to form aspatially long uniform virtual array in which transmitting antennas orreceiving antennas are arranged at equal intervals of 0.5 times awavelength. Otherwise, the antennas must be designed so that asignificant number of virtual array elements overlap spatially. That is,since the degree of freedom of the antenna design is extremely limited,the related art is difficult to be applied to a sparse array, andproblems such as antenna coupling and reduced angle resolution follow.In addition, even though the antennas are designed to satisfy the abovedesign conditions, since the minimum time interval for measuring thephase rotation is T_(chirp), the maximum estimable radial speed does notexceed a physical limit of Equation 2.

A method in which sub-frames having two or more different T_(chirp) areconcatenated and used is disclosed in another related art paper(Wojtkiewicz, Andrzej, et al. “Two-dimensional signal processing in FMCWradars.” disclosed at Proc. XXKKTOiUE (1997):475-480). Here, one frameis composed of several sub-frames. One sub-frame is structurallyidentical to a frame of the conventional TDM FMCW signal. However, sincetwo or more sub-frames are used in this method, there are disadvantagesin that a frame length is too long and data throughput is high. Inaddition, it is difficult to maximize a signal processing gain because adifference in start time between the sub-frames is large and thus signalcoherency is lowered, and it is difficult to properly associate targetsdetected in each sub-frame when a range of the target is greatly changeddue to range migration between the sub-frames.

In order to solve the range migration problem and the coherency problemof the above-descried paper, a method of performing interleaving on atime axis by adding a frequency deviation between sub-frames is proposedin still another related art paper (Kronauge, Matthias, and HermannRohling. “New chirp sequence radar waveform.” disclosed at IEEETransactions on Aerospace and Electronic Systems 50.4 (2014):2870-2877). However, this method is also difficult to be used inpractice because a frame length becomes too long as in the related artdescribed above, even so, this method may be restrictively used onlywhen a sampling rate is very low.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that is further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

The following description relates to proposing a method of increasing alimit of a detectable radial speed of a target at a given number oftransmitting antennas in a time-division-multiplexed (TDM) frequencymodulated continuous wave (FMCW) radar apparatus.

The following description also relates to increasing a detectable radialspeed of a target but not increasing a frame length in a TDM FMCW radarapparatus.

The following description also relates to solving a Doppler ambiguityproblem in a TDM FMCW radar apparatus.

The following description also relates to solving a Doppler ambiguityproblem while minimizing an increase in frame length in a TDM FMCW radarapparatus.

The following description also relates to solving a Doppler ambiguityproblem while minimizing additional constraints in antenna design in aTDM FMCW radar apparatus.

According to one aspect of the proposed invention, transmitting antennasand receiving antennas are arranged such that a plurality of virtualantennas have the same position in a TDM FMCW radar apparatus. At leastthree peculiar chirps, at least one of which is included in a chirp loopof each of waveform signals transmitted by the plurality of virtualantennas having the same position, are respectively positioned inconsecutive time slots and have different periods. A Doppler frequencymay be determined from phase difference values between the at leastthree peculiar chirps respectively positioned in consecutive time slotsmeasured in FMCW radar signals received at the plurality of virtualantennas.

According to an additional aspect, at least three peculiar chirps, whichare respectively positioned in consecutive time slots and have differentperiods, are configured to differ in at least one of an idle timebetween the peculiar chirps or a ramp time of the peculiar chirps.

According to an additional aspect, the at least three chirpsrespectively positioned in consecutive time slots are configured suchthat a sum of an inter-peculiar chirp difference value of the idle timeand an inter-peculiar chirp difference value of the ramp time is limitedby a target maximum detection rate of the target.

According to an additional aspect, a true value of the Doppler frequencymay be determined from a phase difference between the peculiar chirpsmeasured from at least three peculiar chirp signals having a perioddifferent from a measured value. Specifically, a Doppler frequency ofthe aliased spectrum, at which a theoretically calculated phasedifference has the most similar value to the measured phase differencemay be determined as a true Doppler frequency.

In an additional aspect, a search range for the Doppler frequencies ofthe aliased spectrum may be determined by a ratio of the maximum Dopplerfrequency of the target to be detected and of the maximum Dopplerfrequency obtained from a range-Doppler spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an antenna array, which is composed of TXtransmitting antennas and RX receiving antennas, in an exemplaryfrequency modulated continuous wave (FMCW) radar apparatus.

FIG. 2 is a diagram illustrating an example of range-Doppler processingfor estimating a range and a radial velocity from atime-division-multiplexed (TDM) FMCW radar signal.

FIG. 3 illustrates velocity spectra that may be estimated from a Dopplerfast Fourier transform (FFT) output spectrum.

FIG. 4 is a flowchart illustrating a configuration of a signalprocessing method of a TDM FMCW radar apparatus according to anembodiment.

FIG. 5 is a flowchart illustrating a configuration of a spectrumanalysis operation according to an embodiment.

FIG. 6 illustrates a typical frame structure of a radar waveform in theTDM FMCW radar apparatus according to an embodiment.

FIG. 7 illustrates an example of an antenna array to which the proposedinvention may be applied.

FIG. 8 illustrates an example of peculiar chirps, which are respectivelypositioned in consecutive time slots, of waveform signals transmitted byvirtual antennas.

FIG. 9 illustrates another example of peculiar chirps, which arerespectively positioned in consecutive time slots, of waveform signalstransmitted by virtual antennas.

FIG. 10 illustrates a process of obtaining a range-Doppler spectrum byperforming range-Doppler processing in a typical TDM FMCW radarapparatus.

FIG. 11 is a flowchart illustrating a configuration of a Dopplerfrequency determination operation according to an embodiment.

FIG. 12 is a block diagram illustrating a configuration of the TDM FMCWradar apparatus according to an embodiment.

FIG. 13 is a block diagram of a configuration of a spectrum analyzeraccording to an embodiment.

FIG. 14 is a block diagram illustrating a configuration of a Dopplerfrequency determiner according to an embodiment.

DETAILED DESCRIPTION

The foregoing and additional aspects of the present invention will beembodied through the following embodiments described with reference tothe accompanying drawings. It should be understood that variouscombinations of components in each embodiment are possible unlessotherwise specified or contradicted within the embodiment. It will beunderstood that words or terms used in the specification and claimsshould be interpreted as having a meaning that is consistent with theirmeaning in the context of the description and the technical idea of theproposed invention, based on the principle that an inventor is able toproperly define the meaning of the words or terms to best explain theinvention. Hereinafter, exemplary embodiments of the present inventionwill be described in detail with reference to the accompanying drawings.

Description of Claim 1 of Invention

According to one aspect, transmitting antennas and receiving antennasare arranged such that a plurality of virtual antennas have the sameposition in a time-division-multiplexed (TDM) frequency modulatedcontinuous wave (FMCW) radar apparatus. At least three peculiar chirps,at least one of which is included in a chirp loop of each of waveformsignals transmitted by the plurality of virtual antennas having the sameposition, are respectively positioned in consecutive time slots and havedifferent periods. A Doppler frequency may be determined from phasedifference values between the at least three peculiar chirpsrespectively positioned in consecutive time slots measured in FMCW radarsignals received at the plurality of virtual antennas.

FIG. 4 is a flowchart illustrating a configuration of a signalprocessing method of a TDM FMCW radar apparatus according to anembodiment. As illustrated in the drawing, the signal processing methodof the TDM FMCW radar apparatus according to an embodiment includes awireless transmission operation 410, a wireless reception operation 420,a spectrum analysis operation 430, and a Doppler frequency determinationoperation 440.

The proposed invention describes a case of the TDM FMCW radar apparatuscomposed of an array of N_(TX) transmitting antennas and N_(RX)receiving antennas. In this radar apparatus, the wireless transmissionoperation 410 is performed at each transmitting antenna, and thewireless reception operation 420 is performed at each receiving antenna,and the spectrum analysis operation 430 and the Doppler frequencydetermination operation 440 may be performed at all virtual antennas.

According to one aspect, the transmitting antennas and the receivingantennas are arranged such that the plurality of virtual antennas havethe same position. In the wireless transmission operation 410, the radarapparatus transmits an FMCW radar waveform signal through a transmittingantenna array. According to an aspect, at least three peculiar chirps,at least one of which is included in a chirp loop of each of FMCW radarwaveform signals transmitted by the plurality of virtual antennasarranged to have the same position, are configured to be respectivelypositioned in consecutive time slots and have different periods. Here,the expression that three chirps respectively positioned in theconsecutive time slots have different periods includes cases in whichtwo out of three have the same period and the remaining one has adifferent value, or all three have different values.

FIG. 6 illustrates a typical frame structure of a radar waveform in theTDM FMCW radar apparatus according to an embodiment. A frame is a unitof spectrum analysis, and the number of chirp loops included in oneframe is expressed herein as N_(Loop). FIG. 6 illustrates only two chirploops as a part of one frame. In the drawing, T_(loop) is a length ofthe chirp loop. The length of the chirp loop is the period required forall transmitting antennas to transmit a signal once. Each frame iscomposed of one or more chirp loops, and each of the chirp loops iscomposed of one or more chirps. Here, the number of the chirps per chirploop is expressed as N_(TX). The number of the chirps per chirp loop isgenerally equal to the number of the transmitting antennas. When aposition index of the chirp in the chirp loop is expressed as p, p has avalue in a range of 0<=p<=N_(TX)-1.

An upper right end of FIG. 6 illustrates a waveform signal of one chirpperiod of the radar waveform signal. Here,

-   α: frequency sweep rate-   T_(idle,p): idle time of pth chirp-   T_(ramp,p): length of frequency change section of pth chirp-   T_(chirp,p): chirp period of pth chirp (=T_(idle,p) +T_(ramp,p))-   T_(ADC): sampling delay that is time difference between time at    which transmission of chirp starts and time at which sampling starts-   f₀: chirp start frequency.

In the proposed invention, the frequency sweep rate α, the chirp startfrequency f₀, and the sampling delay T_(ADC) are assumed to be the samefor all chirps. When a delay component between a transmitting antennaTX(p) used to transmit the pth chirp and a qth receiving antenna isexpressed as

T_(TX(0), q,)

a value of

T_(TX(0), q)

is determined by azimuth and elevation of a target, and a relativeposition of a virtual antenna specified by TX(p), and q from an antennareference point in space.

FIG. 7 illustrates an example of an antenna array to which the proposedinvention may be applied. When three (TX) transmitting antennas and four(RX) receiving antennas are arranged as illustrated in the drawing, avirtual antenna array Virtual Ant. is illustrated as in the drawing.Each circle represents a position of the virtual antenna and the twodigits indicate a transmitting antenna index and a receiving antennaindex, respectively. Three virtual antennas generated by a transmittingantenna TX₁ and a receiving antenna RX₄, a transmitting antenna TX₂ anda receiving antenna RX₃, and a transmitting antenna TX₃ and a receivingantenna RX₁ are all generated in the same virtual antenna position P.The proposed invention may be applied to a TDM FMCW radar apparatushaving transmitting antennas and receiving antennas arranged such thatthe plurality of virtual antennas have the same position. According toan aspect, at least three peculiar chirps, at least one of which isincluded in a chirp loop of each of waveform signals transmitted by theplurality of virtual antennas having the same position, are respectivelypositioned in consecutive time slots and have different periods. Here,the time slot refers to slots on a time axis distinguished by a chirpcount that is sequentially increased in the chirp loop. In addition, theexpression that the chirps are respectively positioned in theconsecutive time slots means that chirp count values in the chirp loopto which the peculiar chirps belong are sequentially increasing valuesand does not mean that chirps are adjacent to the same chirp loop or thechirps are transmitted sequentially.

In the case of a MIMO radar apparatus, in general, transmitting antennassequentially transmit signals and receiving antennas simultaneouslyreceive signals, and thus, in an example of FIG. 7 , even though FMCWradar waveform signals are received at virtual antennas with a timedifference in the order of the transmitting antenna TX₁ and thereceiving antenna RX₄, the transmitting antenna TX₂ and the receivingantenna RX₃, and the transmitting antenna TX₃ and the receiving antennaRX₁, the FMCW radar waveform signals are buffered in a memory, so thatwhen the signals are processed according to the proposed invention, allof the peculiar chirps respectively positioned in consecutive time slotsmay become available.

According to an aspect, unlike a general waveform signal illustrated inFIG. 6 , each of the chirp loops of the FMCW radar waveform signaltransmitted by the radar apparatus to which the signal processing methodaccording to an embodiment is applied may include at least N_(TX)+1chirps. As an example, the NTX chirps are valid chirps for estimating abeat frequency and a Doppler frequency, and information that determinesthe Doppler frequency may be acquired from at least two consecutivechirps from an N_(TX)th chirp. However, the proposed invention is notlimited thereto, and the consecutive peculiar chirps in the chirp loopmay be positioned at a beginning portion or an intermediate portion ofthe chirp loop.

FIG. 8 illustrates an example of peculiar chirps, which are respectivelypositioned in consecutive time slots, of waveform signals transmitted byvirtual antennas. A peculiar chirp, whose chirp count is three, in avirtual antenna VA1, a peculiar chirp, whose chirp count is four, in avirtual antenna VA2, and a peculiar chirp, whose chirp count is five, ina virtual antenna VA3 are moved onto a virtual time slot VTS. Thesepeculiar chirps have chirp counts in the chirp loop of each radarwaveform signal, but have sequential incremental count values when thesepeculiar chirps gather on the same virtual time slot axis. In thissense, it is expressed herein that peculiar chirps are respectivelypositioned in “consecutive time slots.”

FIG. 9 illustrates another example of peculiar chirps, which arerespectively positioned in consecutive time slots, of waveform signalstransmitted by virtual antennas. A peculiar chirp, whose chirp count isthree, in a virtual antenna VA1, and peculiar chirps, whose chirp countsare four and five, in a virtual antenna VA2 are moved onto a virtualtime slot VTS. The peculiar chirp of “3” and the peculiar chirps of “4and 5” have chirp counts in the chirp loop of each radar waveformsignal, but have sequential incremental count values when these chirpsgather on the same virtual time slot axis. In this sense, it isexpressed herein that peculiar chirps are respectively positioned in“consecutive time slots.”

In the wireless reception operation 420, the radar apparatus receives aFMCW radar waveform signal reflected by the target using the receivingantenna, demodulates a baseband FMCW radar signal, samples a differencesignal between the baseband FMCW radar signal and the transmittedsignal, and transforms the sampled signal into a digital signal andoutputs the same.

In the spectrum analysis operation 430, the radar apparatus determinesand outputs a beat frequency and a Doppler frequency from the signaloutput in the wireless reception operation 420. In one chirp loop, theN_(TX) transmitting antennas sequentially transmit the FMCW radarwaveform signal, and each transmitted FMCW radar waveform signal isreflected by the target and received by the N_(RX) receiving antennas.In the spectrum analysis operation 430, a signal processing circuit ofthe radar apparatus processes the radar waveform signal for eachreceiving antenna. In addition, the signal processing circuit of theradar apparatus processes the waveform signal in units of chirps in thesame time slot in the loops received at one receiving antenna.

In the Doppler frequency determination operation 440, the signalprocessing circuit of the radar apparatus measures phase differencesbetween at least three peculiar chirps, which are respectivelypositioned in consecutive time slots and have different periods,received at the plurality of virtual antennas and determines and outputsa true Doppler frequency from measured values and the Doppler frequencyoutput in the spectrum analysis operation. This will be described indetail below.

Description of Claim 2 of Invention

According to an additional aspect of the proposed invention, at leastthree peculiar chirps, which are respectively positioned in consecutivetime slots and have different periods, are configured to differ in atleast one of an idle time between the peculiar chirps or a ramp time ofthe peculiar chirps. Accordingly, since a phase component generated dueto a Doppler frequency f_(d) in the signal received from the virtualantenna at the same position may be observed at different timeintervals, more information may be obtained. Referring to an exemplarywaveform in a dotted-line circle of FIG. 6 , the idle time between thechirps corresponds to T_(idle), and the ramp time of the chirpcorresponds to T_(ramp). In the example illustrated in the drawing, aperiod of the chirp may be expressed as T_(chirp)=T_(idle)+T_(ramp).

According to the proposed invention, in the three peculiar chirpspresent in the virtual antennas, based on the receiving time, the firstpeculiar chirp may be configured to differ in ramp time, the last(third) peculiar chirp may be configured to differ in idle time, and theintermediate (second) peculiar chirp may be configured to differ in bothramp time and idle time. In the case of employing three or moreconsecutive peculiar chirps, intermediate chirps in time may all beconfigured to differ in both ramp time and idle time.

Similar to that described above, in the illustrated embodiment, in theFMCW radar waveform signal, positions of the peculiar chirps that differin idle time or ramp time, that is, positions on a common time slotaxis, may be the beginning, intermediate, or end of each chirp loop, andthe position or content may be different for each wireless transmitter.In the example illustrated in FIGS. 8 or 9 , the peculiar chirps arepositioned in the middle on a common time slot axis VTS. As will bedescribed below, it is possible to obtain additional informationenabling a true Doppler frequency to be determined from among aplurality of Doppler frequencies, which are generated by an aliasingphenomenon, by varying any one of an idle time T_(idle) between thepeculiar chirps and a ramp time T_(ramp) of the peculiar chirp.

Description of Spectrum Analysis of Claim 4 and FIG. 5

FIG. 5 is a flowchart illustrating a configuration of a spectrumanalysis operation according to an embodiment. As illustrated in thedrawing, in an embodiment, the spectrum analysis operation may include arange FFT processing operation 431, a Doppler fast Fourier transform(FFT) processing operation 433, a range estimation operation 435, and aDoppler estimation operation 437.

In the range FFT processing operation 431, the signal processing circuitof the radar apparatus transforms the digital signal output in thewireless reception operation 420 into a frequency-domain signal in unitsof chirps and outputs the same. Although an FFT transform is selected asan example in the illustrated embodiment, it is understood that theproposed invention encompasses various known transforms forfrequency-domain transformation.

In the Doppler FFT processing operation 433, the signal processingcircuit of the radar apparatus transforms the same frequency componentsof the frequency-domain signal output in the range FFT processingoperation 431 into a frequency-domain signal again and outputs the same.In the Doppler FFT processing operation 433, the signal processingcircuit of the radar apparatus performs inter-chirp processing byperforming FFT after collecting FFT coefficients by frequency, that is,by an FFT index, The transformed FFT coefficients are stored in amemory. The values stored in the memory are range-Doppler spectrumvalues obtained through a range FFT and a Doppler FFT.

In the range estimation operation 435, the signal processing circuit ofthe radar apparatus determines and outputs a beat frequency from thesignal output in the range FFT processing operation 431. In the rangeestimation operation 435, the signal processing circuit of the radarapparatus may search for a position of a peak in the spectrum output inthe range FFT processing operation 431, that is, an index storing amaximum value, to identify a beat frequency, and calculate a range tothe target using the beat frequency.

In the Doppler estimation operation 437, the signal processing circuitof the radar apparatus determines and outputs a Doppler frequency fromthe signal output and stored in the Doppler FFT processing operation433. In the Doppler estimation operation 437, the signal processingcircuit of the radar apparatus may determine the Doppler frequency byidentifying a position of an array that stores a peak value in therange-Doppler spectrum.

Description of Claim 5 of Invention

According to an additional aspect, a true value of the Doppler frequencymay be determined from a phase difference between the peculiar chirpsmeasured from at least three peculiar chirp signals respectivelypositioned in consecutive time slots and having a period different froma measured value. Specifically, a Doppler frequency of the aliasedspectrum, at which a theoretically calculated phase difference has themost similar value to the measured phase difference may be determined asa true Doppler frequency.

Due to the aliased spectrum, the true Doppler frequency is spaced apartfrom the measured Doppler frequency by an integer multiple of a width ofthe aliased spectrum. The phase difference of the at least threepeculiar chirp signals, which are respectively positioned in consecutivetime slots and have different periods, is calculated from the Dopplerfrequency of the aliased spectrum that may be a candidate, and theDoppler frequency whose phase difference is most similar to the actuallymeasured phase difference may be estimated as the true Dopplerfrequency.

Description of FIG. 10

FIG. 10 illustrates a process of obtaining a range-Doppler spectrum byperforming range-Doppler processing in a typical TDM FMCW radarapparatus. Even in the proposed invention, range-Doppler processing isperformed in a manner similar to that shown in FIG. 2 , and adescription is made with reference to the qth receiving antenna as anexample. When a signal processing procedure as illustrated in FIG. 2 isperformed at each receiving channel for all TX(p), a total of N_(TX)range-Doppler spectra may be obtained as shown in FIG. 10 . As indicatedby gray in FIG. 10 , there is a peak in an arrangement corresponding toa range and a radial speed of the target on the range-Doppler spectrum,and a phase value at a peak in the range-Doppler spectrum obtained by aTX(p)→q link, that is, a virtual antenna in which a signal transmittedfrom a pth transmitting antenna is received by the qth receiving antennais, ignoring noise, expressed as follows,

$\phi_{p,q} = 2\pi\left( {f_{0} + \alpha T_{ADC}} \right)\tau_{TX{(p)},q} + 2\pi f_{d}\left( {\sum_{l = 0}^{p - 1}{T_{chirp,t} + T_{idle,p}}} \right)$

-   α: frequency sweep rate-   α: frequency sweep rate-   T_(idle,p): idle time of pth chirp-   T_(ramp,p): length of frequency change section of pth chirp-   T_(chirp,p): chirp period of pth chirp (=T_(idle,p)+T_(ramp,p))-   T_(ADC): sampling delay that is time difference between time at    which transmission of chirp starts and time at which sampling starts-   f₀: chirp start frequency.

Here, when α, f₀, and T_(ADC) are identical for all virtual antennas,and, for signals p, p+1, and p+2 received in the three consecutivechirps,

-   a relationship of-   T_(TX(p), q)=T_(TX(p+1), q)=T_(TX(p+2), q)-   is satisfied,-   (where,-   T_(TX(p), q)-   indicates a delay component between the transmitting antenna TX(p)    and the qth receiving antenna used to transmit the pth chirp)-   phase differences between consecutive chirps may be expressed as    follows,-   $\begin{array}{l}    {\Delta\phi_{1.0} = \phi_{p + 1,q1} - \phi_{p,q0} = 2\pi f_{a}\left( {T_{ramp,p} + T_{idle,p + 1}} \right)\mspace{6mu}\mspace{6mu}\mspace{6mu} + \underset{\Delta T_{idle}}{\underset{︸}{T_{idle,p + 2} - T_{idle,p + 1}}}} \\    {\Delta\phi_{2.1} = \phi_{p + 2,q2} - \phi_{p + 1,q1} = 2\pi f_{a}\left( {T_{ramp,p + 1} + T_{idle,p + 2}} \right)} \\    {\Delta\phi_{2.1.0} = \Delta\phi_{2.1} - \Delta\phi_{1.0} = 2\pi f_{a}(\underset{\Delta T_{ramp}}{\underset{︸}{T_{ramp,p + 1} - T_{ramp,p}}} + \underset{\Delta T_{idle}}{\underset{︸}{T_{idle,p + 2} - T_{idle,p + 1}}})}    \end{array}$

The above case is a case in which all the chirps are received at onevirtual antenna that has received the radar waveform signal transmittedfrom the same transmitting antenna. In another case, even when threechirps, which are included in chirp loops transmitted by the pluralityof virtual antennas having the same position and respectively positionedin consecutive time slots, satisfy the following conditional expression,phase differences may be equally expressed by [Equation 4].

T_(TX(p), q0) = T_(TX(p+1), q1) = T_(TX(p+2), q2)

Here, pth, (p+1)th, and (p+2)th chirps respectively transmitted fromdifferent transmitting antennas TX0, TX1, and TX2 are respectivelyreceived at different receiving antennas q0, q1 and q2. In this case,the virtual antenna generated by the transmitting antenna TX0 and thereceiving antenna q0, the virtual antenna generated by the transmittingantenna TX1 and the receiving antenna q1, and the virtual antennagenerated by the transmitting antenna TX2 and the receiving antenna q2are present by overlapping in the same position.

As another example, even when the following conditional expression issatisfied, phase differences may be equally expressed by [Equation 4].

T_(TX(p), q0) = T_(TX(p+1), q1) = T_(TX(p+2), q1)

Here, the pth chirp transmitted from the different transmitting antennaTX0 is received at the receiving antenna q0, and the (p+1)th chirp andthe (p+2)th chirp transmitted from the transmitting antenna TX1 arereceived at another receiving antenna q1. In this case, the virtualantenna generated by the transmitting antenna TX0 and the receivingantenna q0, and the virtual antenna generated by the transmittingantenna TX1 and the receiving antenna q1 are present by overlapping inthe same position.

To generalize this, it can be seen that, in an antenna array in whichtransmitting antennas and receiving antennas are arranged so that aplurality of virtual antennas have the same position, when at leastthree consecutive peculiar chirps, at least one thereof is included in achirp loop of each of radar signals transmitted by the plurality ofvirtual antennas, are respectively positioned in consecutive time slots,phase differences between the at least three consecutive peculiar chirpsmay be expressed by [Equation 4].

It can be seen from Equation 4 that the phase differences between thechirps respectively positioned in the consecutive time slots aredetermined by an idle time T_(idle) and a ramp Time T_(ramp). When allthe chirps have the same idle time and ramp time as in the conventionalTDM FMCW system, information obtainable from the phase differencesbetween the chirps is limited to 2πf_(d)(T_(ramp)+T_(idle)).

As illustrated in FIG. 10 , in the Doppler processing at the receivingchannel of each virtual antenna, signals received from the sametransmitting antenna are input, and a time difference between the inputsamples is T_(loop). When a Doppler frequency due to a movement of thetarget is expressed as f_(d), the minimum phase difference that may beobserved by performing the Doppler processing is 2πf_(d)T_(loop).

At this point, the maximum Doppler frequency measurable by Equation 1may be expressed as f_(d,max)=1/(2T_(loop)), and in a case off_(d)>|f_(d,max)|, an error occurs in a radial speed estimation valuedue to an aliasing phenomenon as illustrated in FIG. 3 . When theDoppler frequency estimated on the range-Doppler spectrum is expressedas f_(d,measured), and an actual Doppler frequency is expressed asf_(d,true), f_(d,true) and f_(d,measured) have a relationship asfollows,

f_(d, true) = f_(d, measured) + 2kf_(d, max_(.))

In Equation 5, k is an arbitrary integer and k is estimated to determinethe actual Doppler frequency f_(d,true).

FIG. 11 is a flowchart illustrating a configuration of a Dopplerfrequency determination operation according to an embodiment. Asillustrated in the drawing, the Doppler frequency determinationoperation according to an embodiment may include a phase differencemeasurement operation 441, a search range calculation operation 443, andDoppler-frequencies-with-maximum-similarity search operations 445, 447,and 449.

In the phase difference measurement operation 441, the signal processingcircuit of the radar apparatus measures a phase difference between atleast three chirp signals respectively positioned in consecutive timeslots and having different periods. These chirp signals may be signalsextracted from the chirp loops received from different virtual antennas,and some thereof may be signals extracted from the chirp loops receivedfrom the same virtual antenna. These phase difference values may bemeasured by detecting a start point and an end point of each chirp andmeasuring a time difference between the end points of the consecutivechirps. A measurement vector as shown below may be generated from themeasured phase differences by using the phase differences between thechirps obtained in Equation 4,

$X = \begin{bmatrix}{\text{exp}\left( {j\Delta\phi_{1.0}} \right)} \\{\text{exp}\left( {j\Delta\phi_{2.1}} \right)} \\{\text{exp}\left( {j\Delta\phi_{2.1.0}} \right)}\end{bmatrix}_{.}$

In the search range calculation operation 443, the signal processingcircuit of the radar apparatus determines a search range of the Dopplerfrequency of the aliased spectrum by a ratio of a maximum Dopplerfrequency of the target to be detected and a maximum Doppler frequencyobtained from the range-Doppler spectrum.

In Equation 5, a value of k may be referred to as an index of theDoppler frequencies present on the aliased spectrum. There are countlessaliased spectra, and thus, appropriately limiting the range thereof isimportant in terms of the possibility that the proposed invention may beactually applied.

When a start frequency of the FMCW waveform is defined as f₀ and themaximum moving velocity of the target is defined as v_(r,max,target),the maximum Doppler frequency of the target may be expressed as follows,

$f_{d,max,target} = \frac{2v_{r,max,target}}{c}f_{0}$

, (where, c is a wave velocity).

It can be seen from Equation 4 that a minimum measurable time differenceis ΔT_(ramp)+ΔT_(idle). Thus, when ΔT_(ramp)+ΔT_(idle) instead ofT_(loop) is substituted in a conditional expression of Equation 1, andEquation 7 is substituted for f_(d) of Equation 1, which are thenrearranged, the following relational expression may be derived,

$\Delta T_{ramp} + \Delta T_{idle} < \frac{C}{4f_{0}v_{r,max,target}}_{.}$

As shown in Equation 8, in the proposed invention, at least three chirpsrespectively positioned in consecutive time slots are configured suchthat the sum of ΔT_(ramp) and ΔT_(idle), that is, an inter-chirpdifference value of the idle time and an inter-chirp difference value ofthe ramp time, is limited by an aimed maximum detection rate of thetarget. Thus, using the maximum detection rate determined by the systemdesign requirements, one or both of ΔT_(ramp) and ΔT_(idle) areappropriately adjusted to satisfy the relationship of Equation 8.

As shown in FIG. 3 and Equation 5, a peak due to the aliasing phenomenonoccurs at intervals of 2f_(d,max) on the Doppler spectrum. Thus, aninteger, which is greater than or equal to a ratio of Equations 7 and2f_(d,max) but is smallest, is determined as the maximum value of k.

$k_{MAX} = \left\lceil \frac{f_{d,max,target}}{2f_{d,max}} \right\rceil$

where, 2f_(d,max,target) is the maximum Doppler frequency to bedetected, and 2f_(d,max) is the maximum Doppler frequency that may bemeasured through the Doppler processing, that is, a Doppler FFT. Thatis, k that maximizes Re{w(k)^(H)x} is identified while changing k from-k_(MAX) to k_(MAX) within a range of 2f_(d,max,target) from a Dopplerfrequency of 2f_(d,measured), which is primarily measured through theDoppler processing.

In the Doppler-frequencies-with-maximum-similarity search operations445, 447, and 449, the signal processing circuit of the radar apparatusdetermines and outputs the Doppler frequency, at which a theoreticallycalculated phase difference is most similar to the measured phasedifference, from among the Doppler frequencies of the aliased spectrum.

First, at a search target Doppler frequency, a phase difference betweenat least three chirp signals, which are respectively positioned inconsecutive time slots and have different periods, included in the chirploop is theoretically calculated, and a similarity value between thetheoretically calculated value and the measured value measured in thephase difference measurement operation 441 is calculated (operation445). For all the Doppler frequencies, which are included in the aliasedspectrum, within the search range, the Doppler frequency with themaximum value among the calculated similarity values is retrieved (447),and the retrieved Doppler frequency is output as the true Dopplerfrequency (449).

In order to compare the measured value with the theoretically calculatedresult, the theoretical value is defined as follows by using Equations 4and 5,

$W(k) = \begin{bmatrix}{\exp\left( {j2\pi f_{d,measured} + 2k\left| f_{d,max} \right|} \right)\left( \left( {T_{ramp,p} + T_{idle,p + 1}} \right) \right)} \\{\exp\left( {j2\pi f_{d,measured} + 2k\left| f_{d,max} \right|} \right)\left( \left( {T_{ramp,p + 1} + T_{idle,p + 2}} \right) \right)} \\{\exp\left( {j2\pi f_{d,measured} + 2k\left| f_{d,max} \right|} \right)\left( \left( {\Delta T_{ramp} + T_{idle}} \right) \right)}\end{bmatrix}$

Since k, which has the highest degree of similarity between thetheoretical value of Equation 10 and the measured value of Equation 6,is the solution, k that maximizes Re{w(k)Hx} is identified by changing kwithin an appropriate range, and the actual Doppler frequency iscalculated by substituting the estimation result into Equation 5. Here,H is a Hermitian operator. Thereafter, from the Doppler frequency, aradial speed of the target is calculated using a relationship ofv_(r,true) = λf_(d,true)/2.

Description of Invention of Apparatus Description of Claim 7 ofInvention

FIG. 12 is a block diagram illustrating a configuration of the TDM FMCWradar apparatus according to an embodiment. As illustrated in thedrawing, the TDM FMCW radar apparatus according to an embodimentincludes a wireless transmitter 610, a wireless receiver 630, a spectrumanalyzer 650, and a Doppler frequency determiner 670. In the illustratedembodiment, N_(TX) wireless transmitters, N_(RX) wireless receivers, andN_(TX)*N_(RX) spectrum analyzers are included. That is, since thespectrum analyzer must be provided for each virtual antenna, the N_(TX)spectrum analyzers are connected to each wireless receiver. However, forsimplicity of illustration, only one wireless transmitter 610, onewireless receiver 630, two spectrum analyzers 650-1 and 650-2, and twoDoppler frequency determiners 670-1 and 670-2 are specified in thedrawings.

According to an aspect, the transmitting antennas and the receivingantennas are arranged such that the plurality of virtual antennas havethe same position. The wireless transmitter 610 transmits an FMCW radarwaveform signal through a transmitting antenna. According to an aspect,in the FMCW radar waveform signals transmitted by the wirelesstransmitter 610 using transmitting antennas constituting the pluralityof virtual antennas having the same position, each chirp loop has atleast one peculiar chirp, and there are at least three peculiar chirps.These peculiar chirps are respectively positioned in consecutive timeslots when viewed on a common time slot axis, and the at least threepeculiar chirps have different periods. Here, the expression that threepeculiar chirps respectively positioned in the consecutive time slotshave different periods includes cases in which two out of three have thesame period and the remaining one has a different value, or all threehave different values.

The wireless receiver 630 receives FMCW radar waveform signals reflectedby the target using the receiving antenna, demodulates baseband FMCWradar signals, samples a difference signal between the baseband FMCWradar signal and the transmitted signal, and transforms the sampledsignal into a digital signal and outputs the same. The transmittingantennas and the receiving antennas are generally linearly arranged atequal intervals, but may also be non-linearly arranged at non-uniformintervals.

The spectrum analyzer 650 determines and outputs beat frequencies andDoppler frequencies from the signal output from the wireless receiver630. In one chirp loop, the N_(TX) transmitting antennas sequentiallytransmit the FMCW radar waveform signal, and each transmitted FMCW radarwaveform signal is reflected by the target and received by the N_(RX)wireless receivers. Each spectrum analyzer 650 processes the chirps of aperiod corresponding to the wireless transmitter 610 allocated theretoamong the chirps output from the wireless receiver 630. For example, thespectrum analyzer 650-1 may be allocated to process first chirps of theN_(TX) chirps that are repeated for each chirp loop, and the spectrumanalyzer 650-2 may be allocated to process second chirps of the N_(TX)chirps that are repeated for each chirp loop.

The Doppler frequency determiner 670 measures a phase difference betweenat least three chirps, which are respectively positioned in consecutivetime slots and have different periods, received from the wirelessreceiver 630 and determines and outputs a true Doppler frequency valuefrom the measured values and the Doppler frequency output in thespectrum analysis operation. This will be described in detail below.

Description of Claim 8 of Invention

In an additional aspect of the proposed invention, the at least threechirps respectively positioned in the consecutive time slots areconfigured to differ in at least one of an idle time between the chirpsor a ramp time of the chirp. Accordingly, phase components generated dueto a Doppler frequency f_(d) may be observed at different time intervalsso that more information may be obtained. Referring to an exemplarywaveform in a dotted-line circle of FIG. 6 , the idle time between thechirps corresponds to T_(idle), and the ramp time of the chirpcorresponds to T_(ramp). In the example illustrated in the drawing, aperiod of the chirp may be expressed as T_(chirp)=T_(idie)+T_(ramp).

According to the proposed invention, in the at least three chirpsrespectively positioned in consecutive time slots and having differentperiods, a first chirp may be configured to differ in ramp time, a lastchirp may be configured to differ in idle time, and an intermediatechirp may be configured to differ in both ramp time and idle time. Inthe case of employing three or more chirps respectively positioned inconsecutive time slots and having different periods, intermediate chirpsmay be configured to differ in both ramp time and idle time.

Similar to that described above, in the illustrated embodiment, in theFMCW radar waveform signal, positions of the chirps, which differ inidle time or ramp time, may be the beginning, middle, or end of theloop, and the position or content may be different for each wirelesstransmitter. As will be described below, it is possible to obtainadditional information enabling a true Doppler frequency to bedetermined from among a plurality of Doppler frequencies, which aregenerated by an aliasing phenomenon, by varying an idle time T_(idle)between the chirps and a ramp time T_(ramp) of the chirp.

Description of Claim 10 of Invention

FIG. 13 is a block diagram of a configuration of a spectrum analyzeraccording to an embodiment. As illustrated in the drawing, in anembodiment the spectrum analyzer 650 includes a range FFT processor 651,a range estimator 652, a Doppler FFT processor 655, and a Dopplerestimator 654.

The range FFT processor 651 transforms the digital signal output fromthe wireless receiver 630 into a frequency-domain signal in units ofchirps and outputs the same. Although an FFT transform is selected as anexample in the illustrated embodiment, it is understood that theproposed invention encompasses various known transforms forfrequency-domain transformation. The range FFT processor 651 performsFFT transform on a beat frequency signal of the chirp transmitted by theantenna allocated thereto among the chirps, which are present in a firstchirp loop of the digital signal output by the wireless receiver 630connected thereto, and stores the transformed signal in a range FFTbuffer 653, and performs FFT transformation on a beat frequency signalof the chirp, which is transmitted by the same antenna, in the nextchirp loop and stores the transformed signal in the range FFT buffer653. Thus, in the illustrated embodiment, the range FFT processor 651processes the FFT transformation as many times as the number of thechirp loops, that is, N_(Loop) times, and the range FFT buffer 653 has asize capable of storing at least N_(Loop) FFT coefficient sets.

Although an example in which N_(Loop) range FFT processors 210 arepresent is illustrated in FIG. 2 , the embodiment illustrated in FIG. 10adopts a structure in which one range FFT processor 651 is provided foreach virtual antenna, and performs FFT transform on the beat frequencysignal from the signal, which is received by the receiving antenna, foreach chirp loop, and outputs a result and the result is accumulated andstored in the range FFT buffer 653. Accordingly, the range FFT processor651 should have a speed at which a single Fourier operation may be fullyprocessed within a period of at least one chirp loop.

The range estimator 652 determines and outputs a beat frequency from thesignal output from the range FFT processor 651. The range estimator 652may search for a position of a peak, that is, an index storing themaximum value in the spectrum stored in the range FFT buffer 653 toidentify the beat frequency, and calculate a range to the target fromthe beat frequency.

The Doppler FFT processor 655 transforms the same frequency componentsof the frequency-domain signal output from the range FFT processor 651into a frequency-domain signal again and outputs the same. The DopplerFFT processor 655 performs inter-chirp processing by performing FFTtransformation by collecting FFT coefficients, which are stored in therange FFT buffer 653, by frequency, that is, by an FFT index. Thetransformed FFT coefficients are stored in a Doppler FFT buffer 657.

In one embodiment, the Doppler FFT processor 655 includes as many FFTtransformers as the number of Fourier coefficients stored in the rangeFFT buffer 653. As another example, a structure of repeatedly executingone Fourier transform may be employed.

The Doppler FFT processor 655 receives N_(Loop) output coefficients ofthe same frequency corresponding to the number N_(Loop) of the chirploops and performs FFT transformation on the output coefficients andstores the transformed output coefficients in the Doppler FFT buffer657. The values stored in the Doppler FFT buffer 657 are range-Dopplerspectrum values obtained through a range FFT and a Doppler FFT.

The Doppler estimator 654 determines and outputs a Doppler frequencyfrom the signal output from the Doppler FFT processor 655. The Dopplerestimator 654 may determine the Doppler frequency by identifying aposition of an array that stores a peak value from the range-Dopplerspectrum stored in the Doppler FFT buffer 657

Description of Claim 11 of Invention

According to an additional aspect, a true value of the Doppler frequencymay be determined from a phase difference between the chirps measuredfrom at least three chirp signals respectively positioned in consecutivetime slots and having a period different from a measured value.Specifically, a Doppler frequency of the aliased spectrum, at which atheoretically calculated phase difference has the most similar value tothe measured phase difference may be determined as a true Dopplerfrequency.

The Doppler frequency determiner 670 measures a phase difference betweenchirps from at least three chirp signals, which are respectivelypositioned in consecutive time slots, output from the wireless receiver630 as shown in FIG. 6 , receives the plurality of Doppler frequenciescalculated by the Doppler estimator 654, and determines and outputs theDoppler frequency, at which the measured phase difference is closest tothe theoretically calculated value, as a true value from among theplurality of Doppler frequencies. Since these operations have beenpreviously described with reference to FIG. 11 , detailed descriptionsthereof will be omitted.

FIG. 14 is a block diagram illustrating a configuration of the Dopplerfrequency determiner according to an embodiment. As illustrated in thedrawing, the Doppler frequency determiner includes a phase differencemeasurer 671, a search range calculator 673, and a Doppler frequencysearcher 675.

The phase difference measurer 671 measures the phase differenceexpressed by Equation 4, that is, the phase difference between the atleast three chirps respectively positioned in consecutive time slots.These phase difference values may be measured by detecting a start pointand an end point of each of the chirps and measuring a time differencebetween the end points respectively positioned in consecutive timeslots.

The search range calculator 673 determines a search range of the Dopplerfrequency of the aliased spectrum by a ratio of the maximum Dopplerfrequency of the target to be detected and the maximum Doppler frequencyobtained from the range-Doppler spectrum.

The Doppler frequency searcher 675 determines and outputs the Dopplerfrequency, at which a theoretically calculated phase difference value ismost similar to a measured phase difference value, from among theDoppler frequencies of the aliased spectrum corresponding to the searchrange calculated by the search range calculator 673.

First, at a search target Doppler frequency, a phase difference betweenat least three chirp signals, which are respectively positioned inconsecutive time slots and have different periods, included in the chirploop is theoretically calculated, and a similarity value between thetheoretically calculated value and the measured value measured by thephase difference measurer 671 is calculated. For all the Dopplerfrequencies, which are included in the aliased spectrum, within thesearch range, the Doppler frequency with the maximum value among thecalculated similarity values is retrieved, and is output as the trueDoppler frequency.

The operation of the configuration of FIG. 14 has been described in themethod invention described with reference to FIG. 11 , and thus detaileddescription thereof will be omitted.

According to the proposed invention, it is possible to overcome theexisting limit of a detectable radial velocity of a target in a TDM FMCWradar apparatus. Furthermore, according to the proposed invention, it ispossible to increase position resolution by increasing the number oftransmitting antennas in a TDM FMCW radar apparatus. Furthermore, it ispossible to solve a Doppler ambiguity problem while minimizingconstraints in antenna design or minimizing an increase in frame lengthin a TDM FMCW radar apparatus. Alternatively, according to the proposedinvention, it is possible to solve a Doppler ambiguity problem whileminimizing constraints in antenna design and minimizing an increase inframe length in a TDM FMCW radar apparatus.

The present invention has been described above with reference to theembodiments referring to the accompanying drawings, but is not limitedthereto. Rather, the present invention should be construed asencompassing various modifications that may be apparent to those skilledin the art. The appended claims are intended to cover suchmodifications.

What is claimed is:
 1. A signal processing method of atime-division-multiplexed (TDM) frequency modulated continuous wave(FMCW) radar apparatus having an antenna array in which transmittingantennas and receiving antennas are arranged such that a plurality ofvirtual antennas have the same position, the method comprising: awireless transmission operation of transmitting FMCW radar waveformsignals that are configured such that at least three peculiar chirps, atleast one thereof is included in a chirp loop of each of radar signalstransmitted by the plurality of virtual antennas, are respectivelypositioned in consecutive time slots and have different periods; awireless reception operation of demodulating baseband FMCW radar signalsfrom FMCW radar waveform signals reflected by a target, samplingdifference signals between the baseband FMCW radar signals and thetransmitted signals, transforming the difference signals into digitalsignals, and outputting the digital signals; a spectrum analysisoperation of determining and outputting beat frequencies and Dopplerfrequencies from the signals output in the wireless reception operation;and a Doppler frequency determination operation of measuring phasedifferences between the at least three peculiar chirps, which arerespectively positioned in consecutive time slots, have differentperiods, and are received at the plurality of virtual antennas in thewireless reception operation, and determining and outputting a trueDoppler frequency from the measured values and the Doppler frequenciesoutput in the spectrum analysis operation.
 2. The method of claim 1,wherein the FMCW radar waveform signals transmitted in the wirelesstransmission operation are configured such that the at least threepeculiar chirps respectively positioned in consecutive time slots differin at least one of an idle time between the peculiar chirps or a ramptime of the peculiar chirps.
 3. The method of claim 2, wherein the atleast three chirps respectively positioned in consecutive time slots areconfigured such that a sum of an inter-peculiar chirp difference valueof the idle time and an inter-peculiar chirp difference value of theramp time is limited by a target maximum detection rate of the target.4. The method of claim 1, wherein the spectrum analysis operationincludes: a range fast Fourier transform (FFT) processing operation oftransforming the digital signal output in the wireless receptionoperation into a frequency-domain signal in units of chirps andoutputting the frequency-domain signal; a Doppler FFT processingoperation of transforming the same frequency components of thefrequency-domain signal output in the range FFT processing operationinto a frequency-domain signal again and outputting the frequency-domainsignal; a range estimation operation of determining and outputting abeat frequency from the signal output in the range FFT processingoperation; and a Doppler estimation operation of determining andoutputting a Doppler frequency from the signal output in the Doppler FFTprocessing operation.
 5. The method of claim 1, wherein in the Dopplerfrequency determination operation, a phase difference between thepeculiar chirps is measured from at least three peculiar chirp signals,which are respectively positioned in consecutive time slots and outputin the wireless reception operation, and the Doppler frequency, at whichtheoretically calculated phase difference values are most similar tomeasured phase difference values, is determined as the true Dopplerfrequency and output.
 6. The method of claim 1, wherein the Dopplerfrequency determination operation includes: a phase differencemeasurement operation of measuring phase differences between the atleast three peculiar chirps respectively positioned in consecutive timeslots and having different periods; a search range calculation operationof determining a search range of Doppler frequencies of an aliasedspectrum by a ratio of a maximum Doppler frequency of the target to bedetected and a maximum Doppler frequency obtained from a range-Dopplerspectrum; and a Doppler frequency search operation of determining andoutputting a Doppler frequency at which a theoretically calculated phasedifference value is most similar to a measured phase difference value,from among the Doppler frequencies of the aliased spectrum.
 7. Atime-division-multiplexed (TDM) frequency modulated continuous wave(FMCW) radar apparatus, comprising: an antenna array in whichtransmitting antennas and receiving antennas are arranged such that aplurality of virtual antennas have the same position; a wirelesstransmitter configured to transmit FMCW radar waveform signals that areconfigured such that at least three peculiar chirps, at least onethereof is included in a chirp loop of each of radar signals transmittedby the plurality of virtual antennas, are respectively positioned inconsecutive time slots and have different periods; a wireless receiverconfigured to demodulate baseband FMCW radar signals from FMCW radarwaveform signals reflected by a target, sample difference signalsbetween the baseband FMCW radar signals and the transmitted signals, andtransform the difference signals into digital signals and output thedigital signals; a spectrum analyzer configured to determine and outputbeat frequencies and Doppler frequencies from the signal output from thewireless receiver; and a Doppler frequency determiner configured tomeasure phase differences between the at least three peculiar chirps,which are respectively positioned in consecutive time slots, havedifferent periods, and are received from the plurality of virtualantennas by the wireless receiver, and determine and output a trueDoppler frequency from the measured values and the Doppler frequenciesoutput from the spectrum analyzer.
 8. The TDM FMCW radar apparatus ofclaim 7, wherein the FMCW radar waveform signals transmitted by thewireless transmitter are configured such that the at least three chirpsrespectively positioned in consecutive time slots differ in at least oneof an idle time between the peculiar chirps or a ramp time of thepeculiar chirps.
 9. The TDM FMCW radar apparatus of claim 8, wherein theat least three chirps, which are respectively positioned in consecutivetime slots, are configured such that a sum of an inter-chirp differencevalue of the idle time and an inter-chirp difference value of the ramptime is limited by a target maximum detection rate of the target. 10.The TDM FMCW radar apparatus of claim 7, wherein the spectrum analyzerincludes: a range fast Fourier transform (FFT) processor configured totransform the digital signal output from the wireless receiver into afrequency-domain signal in units of chirps and output thefrequency-domain signal; a Doppler FFT processor configured to transformthe same frequency components of the frequency-domain signal output fromthe range FFT processor into a frequency-domain signal again and outputthe frequency-domain signal; a range estimator configured to determineand output a beat frequency from the signal output from the range FFTprocessor; and a Doppler estimator configured to determine and output aDoppler frequency from the signal output from the Doppler FFT processor.11. The TDM FMCW radar apparatus of claim 7, wherein the Dopplerfrequency determiner measures a phase difference between the peculiarchirps from at least three peculiar chirp signals, which arerespectively positioned in consecutive time slots and output from thewireless receiver, and determines and outputs the Doppler frequency, atwhich theoretically calculated phase difference values are most similarto measured phase difference values, as the true Doppler frequency. 12.The TDM FMCW radar apparatus of claim 7, wherein the Doppler frequencydeterminer includes: a phase difference measurer configured to measurethe phase differences between the at least three peculiar chirpsrespectively positioned in consecutive time slots and having differentperiods; a search range calculator configured to determine a searchrange of Doppler frequencies of an aliased spectrum by a ratio of amaximum Doppler frequency of the target to be detected and a maximumDoppler frequency obtained from a range-Doppler spectrum; and a Dopplerfrequency searcher configured to determine and output a Dopplerfrequency at which a theoretically calculated phase difference value ismost similar to a measured phase difference value, from among theDoppler frequencies of the aliased spectrum.